A popular form of windows is a casement window which includes a master frame fixed to the structure such as a building or house and a casement frame which carries the window. The master frame and casement frame are hinged together by concealed hinges along the top and bottom. One side of the window generally includes a manual lock. During the opening and closing of the window the casement frame moves in an irregular path until it engages the master frame. Various devices have been provided to attempt to seal the casement frame to the master frame in the closed position. Heretofore no satisfactory device has been provided along the side of the casement window opposite its manual lock. Accordingly, under severe wind conditions there frequently results a bulging or bellying-out of the casement frame from the master frame along the unlocked side.